Markedly Enhanced Levels of Peroxyacetyl Nitrate (PAN) During COVID‐19 in Beijing

Abstract

Abstract High levels of secondary air pollutants during COVID‐19 in China have aroused great concern. In Beijing, measured daily mean peroxyacetyl nitrate (PAN) concentrations reached 4 ppb over the lockdown period (24 January to 15 February), whose averages were 2–3 times that before lockdown (1–23 January). The lockdown PAN levels also reached a high historical record based on our long‐term measurements (2016–2019). Unlike ozone and PM 2.5 , PAN formation depends on less complex photochemistry between NO x and volatile organic compounds (VOCs), providing a novel approach to investigate the wintertime photochemistry during COVID‐19. The GEOS‐Chem simulations suggest a markedly enhanced photochemistry by a factor of 2 during the lockdown. Change of meteorology featuring with anomalous wind convergence under higher temperatures is the main reason for enhanced photochemical formation of PAN, while chemically nonlinear feedbacks also play a role. Our results suggest implementing targeted VOC emission controls in the context of increasing photochemical pollution over this complex polluted region.